1. Field of the Invention
The present invention relates to dredges and more particularly to cutter elements rotatably disposed upon the end portion of a dredge boom that carries a suction pipe for dredging in a marine environment. Even more particularly, the present invention relates to an improved dredge apparatus and more particularly to an improved rotary cutter element that includes a least a pair of spaced apart circular rings, each having an open center and the pair of rings defining an inlet and an outlet for material to be dredged. The combination of rings define a frame that supports a plurality of helical vanes, each of the vanes extending circumferentially around the rings joining the rings to form a frame therewith and extending from one ring to the next along a helical path, and wherein the rings have a V-shaped transverse cross section providing a concave surface that faces the suction.
2. General Background
Suction dredges are commercially available devices that include a floating barge, an elongated movable boom having a free end and a rotary cutter element or cutter head that is supported at the free end of the boom. The hull portion of the dredge can be held in a fixed position using spuds or anchors or the like. The boom end portion moves with the cutter head to dislodge material that is to be suctioned from the dredge site. The boom typically pivots at its connection to the dredge hull.
Suction dredges have been used to excavate natural material such as is found on river bottoms, lake bottoms and sea beds. However, suction dredges have also been used for clean-up of hazardous waste pits which contain slurried or viscous materials such as for example the refuse of chemical plants, petro-chemical plants, oil and gas well drilling operations and the like. In the clean up of hazardous wastes, the material can be very viscous and difficult to remove using conventional cutter heads and conventional suction dredges.
There exists a need for an improved dredge apparatus including an improved rotary cutter head element that can efficiently remove the viscous material found in hazardous waste dumps and like situations.
Many rotary cutter heads and suction dredges have been patented. Examples of recent patents that relate to cutter heads and suction dredges are U.S. Pat. Nos. 3,807,066; 4,135,318; and 4,702,024. The '066 patent issued to Norman Proehl and entitled "Cutter Head for Suction Dredge" discloses a conical cutting head for use with a suction dredge. The apparatus includes wearing parts and strength members which may be easily assembled and removed for replacement. The cutter head has blades directly attached to strengthening struts with the blades inclined in the direction of rotation of the head. Cutter teeth which extend radially outwardly beyond the blade are also attached directly to the struts. Both the struts and the blades are formed of straight pieces of material of conventional cross sections such as rectangular or square, which have been cut to fit. Lifter plates are provided in the cutter head between the hub and blade to move material to the inlet of the suction mouth.
U.S. Pat. No. 4,135,318 issued to Voldeda provides a generally conical cutter head for an underwater dredger that includes a plurality of helical cutting arms having teeth mounted thereon. The arms are fixed at one end to a hub and at the other end to a base ring. The tooth spacing between the respective cutting arms is arranged in a multi-staggered configuration whereby each tooth removes a symmetrical piece of soil and is not subjected to loads parallel to the local section of the contour line.
U.S. Pat. No. 4,702,024 discloses a dredging helical cutter suited for use for example with a dredger equipped with scope-in plates. Earth and sand is transported by helical vanes to a send-out end portion of helical cutter. The scope-in plates transport the earth and sand to an opening of an earth/sand suction tube. The opening of the suction tube is provided and a portion of the helical cutter for receiving a rotary shaft. All of the earth and sand excavated by the helical cutter can therefore be sucked into the suction tube and the efficiency of the dredging operation can be greatly increased by a simple structure.
Other older patents have issued that relate to cutters and suction dredges. Examples of such older patents include the Hughes U.S. Pat. No. 1,477,352 entitled "Dredge Cutter" providing a spiral blade supporting vanes, a cutting blade secured at the inner surface of each of the vanes and conforming in curvature to the latter, the spiral of the blade being such that it rear travels circumferentially in advance of its forward extremity.
Another older patent is the Olhlahusen U.S. Pat. No. 2,999,324 entitled "Cutters for Hydraulic Dredges". The Olhlahusen patent discloses a cutter comprising a supporting frame including a hub adapted to be rotated about an axis at the center thereof, a plurality of struts extending therefrom and diverging from each other, the ends of the struts being secured to an annular base member, a cutting cage positioned to substantially envelop the frame, the cutting cage including a plurality of annular spaced members being connected by a plurality of web members, said annular members having outwardly extending cutting teeth, the inner portion of said annular members having recessed portions in which said struts of the supporting frame are positioned.
Foreign patents that relate to dredges a cutter heads include French Patent Nos. 401,596 and 348,363; a Japanese Patent No. 57-89035; and Russian Patent Nos. SU412350 and SU382795. The Japanese Patent has a cutter head with multiple rings that include multiple blades between them for rotary dredges. The structure includes an upper cutter and a lower cutter that are connected into a monolithic cutter at a connection an opening end of mud suction pipe inserted into the cutter mounted at the proximity of the connection and the upper and lower cutters rotatably installed at the mud suction pipe. The cutter twistings are formed in a reverse direction to that of the opposite, whereby mud, excavated by the upper cutter, is pushed downward through the rotation of the cutter and mud excavator by the lower cutter is pushed upward through the turning of the center. This permits the smooth operation of the cutter even is a ratio of the length to the diameter of the cutter is set to 1.2 or more.